1. Field of the Invention
The present invention relates to a closed-caption scrolling method and apparatus, and more particularly, to a closed-caption scrolling method and apparatus whereby character and control codes are encoded in a television signal to be transmitted as a caption broadcasting signal, and then received to be displayed on a screen of a television receiver by selection of a viewer.
2. Description of the Related Art
The caption broadcasting system in television broadcasting can be classified into an open caption system for displaying a caption of emergency news, announcements, etc., on a television screen by selection of a broadcaster by superimposing the caption signal in an active period of a television signal, and a closed caption system for displaying a caption of words on the screen by selection of a viewer by encoding the caption signal in a non-active period, i.e., in a vertical blanking interval of the television signal.
The closed-caption broadcasting has been carried out in the United States since 1978 for people who have difficulty in hearing and cannot recognize the words of the scene without sign language. The closed-caption broadcasting is also useful in studying a foreign language.
The U.S. Pat. No. 5,294,982 issued on March, 1994 discloses a closed-caption broadcasting system suitable for displaying Roman characters and syllable characters. Especially, captioning of the syllable characters such as Korean is explained in detail in this patent. According to this patent, in order to broadcast Hangul (Korean alphabet) as a closed-caption, one Hangul character is separated into initial, medial, and final consonant phonemes and ASCII (American Standard Code for Information Interchange) codes corresponding to the respective consonant phonemes are transmitted. In a receiving part, the ASCII codes are received and decoded, and then the initial, medial, and final consonant phonemes are mapped to form and display the Hangul character.
However, according to this conventional Hangul closed-captioning system, since at least two or three bytes of data should be used for representing one Hangul character, the transmission speed and the display speed thereof become lowered. Also, its decoding process becomes complicated because the position of one Hangul character is searched by combination of three or four bytes of data, causing the cost of a caption decoder to increase.
Also, the conventional Hangul closed-captioning system has difficulty in simultaneously displaying Chinese characters, Hangul, and Japanese, and in simultaneously displaying English, Russian and Greek, as well as in displaying special symbols.
Also, since a control code is required in case of displaying word information between additional information and then displaying additional information again, there is no independence between the word information and additional information, and the control system for discriminating a display mode of the word information becomes complicated. If the display mode control code is not received at the start point of the receiving device's operation, the word information cannot be displayed until a next control code is received.
Further, since the conventional system has been developed based on the television broadcasting environment in the United States, it shows an inferior receiving state in the geographic setting of Korea that has mountainous districts over 70%, thereby deteriorating the quality of the caption display.
Also, a pop-on function may be adopted in displaying the caption words. According to the pop-on function, since the data is first stored in a receiving buffer and then displayed according to an `on-display` control code, it is required that the receiving buffer includes a receiving page and a display page. Accordingly, the memory capacity of the receiving buffer should be increased, thereby causing the cost of the receiver to be increased.
Meanwhile, related arts regarding the closed-caption broadcasting and receiving apparatuses are disclosed in U.S. Pat. Nos. 5,327,176, 4,310,854, 5,347,365, 5,249,050, 5,374,960, and 5,315,386, and Japanese Patent Laid-open Nos. 6-165065 and 6-165064.